Grinding wheel



. cRoMPTvoN, JR 2,148,400

GRINDING WHEEL Feb. 2l, 1939.

Filed Janv. 1s, 1938 Eli dii

Patented Feb. 2l,A 1939 `UNITED STATES PATENT OFFICE GRINDING WHEELGeorge Crompton, Jr., Worcester, Mass., assignor to Norton Company,Worcester, Mass., a. corporation. ot Massachusetts `Application January13, 1938, Serial N0. 184,749

`Claims. (Gl. Eil- 273) The invention relates to grinding wheels, and

with regard to its more specific features to cutting-ofi Wheels.

One object of the invention is to provide a sharper cutting-01T wheel..Another object of the hitherto 4been provided. Another'object or theinvention is to form a grinding wheel with cutting edges which simulatethe action of a lathe. Another object ci the invention is to provide agrinding wheel having oriented abrasive oi any desired thickness.

Other objects will be in part obvious or in part pointed outhereinafter'.

The invention accordingly consists in the features of construction,combinations of elements, arrangements of parts, and'in the severalsteps and relation and order of yeach of said steps to one or more ofthe others thereof, all as will be illustratively described herein, andthe scope oi the application oi which will be indicated in the followingclaims.

In the accompanying drawing, in which is illustrated one of manypossible embodiments oi the mechanical features oi this invention,

Figure l is a longitudinal cross sectional view of a mold for producingthe abrasive aggregates used in making :the grindingv wheel of theinvention.

Figure 2 is a transverse sectional view of the mold of Figure 1, takenon the line 2--2 of Figure l.

Figure 3 is a perspective view of the abrasive stick produced by themold of Figures l. and 2.

Figure 4 is an elevation of apparatus for breaking oi short pieces ofthe stick of Figure 3, thereby producing abrasive aggregates consistingof triangular prisms.

Figure 5 is a verticalv sectional view of a rotating mold apparatuswhich is preferably used in carrying out the invention.

Figure 6 is an enlarged view ot the mold of Figure 5 after it has beenfilled and just preparatory to pressing.

Figure 7 is a fragmentary transverse sectional View of the completedarticle.

Figure 8 is a fragmentary axial sectional view of a multilayer grindingWheel accordance with the invention.

constructed in Referring first to Figures l and 2, I provide a moldcomprising a rectangular parallelepiped outer mold ring it having arectangular parallelepipedal hole in which are inserted side moldsections i i and 'i2 and a top mold member I3 5 which is 'i' shaped incross section, as shown in Figure 2. The cavity It oi the moldterminates in a V shapcdbottom iii, the apex of the dihedral angle ofwhich forms the dividing line between the sidemold sections ii and i2.The bottom 1o of the top mold plate il! constitutes an elongated narrowplane surface.

I provide a mixture of abrasivegrain and suitu able bond. A grindingwheel mixture ofy any desired type is contemplated bythe: present inldvention. PreferablyI use vitriable bond, that is to say a mixture ofappropriate clays and a temporary binder, if desired.' A suitable amountof moisture may be incorporated in the mix. Preparation-of mixes ofclays, temporary binders and 2oplace this in a mixing pan and wet thegrain with water. I then add a powdered mixture oi clays, for exampleincluding ball clay, slip clay and feldspar. I then edect a mixing,adding a small quantity of temporary binder, such as dextrlne, duringthe mixing.

After this mixing of the abrasive grains and the bond is achieved, Iplace a definite quantity oi' the mixture in the space ill of the moldof Figures l and 2. I then transfer the mold to a hydraulic press andpress the plate id downwardly. I then strip the mold in any suitable suWay, this mold being readily separable as is apparent from itsconstruction. In pressing the` mixture in the mold space M, I mayprecalculate the volume percentage of abrasive grain and bond and poresto achieve a desired structure. When the mold parts Il, i2 and I3 areremoved from the mold ring i0, the pressed mixture which is in the formof a green abrasive stick I5 shown in Figure 3 is readily removed.' Itake this stick with others of like character to a. ceramic kiln andvitrify at an appropriate tem'- perature, for example of the order ofcone l2. After the required period of firing, the stick i5 `is avitrified abrasive stick constituting a tribearings 54 and 55.

an equilateral triangle according to the preferred form of theinvention.

Referring now to Figure fi, I provide an apparatus comprising an anvil28 having a hole 2| therethrough which is triangular in cross sectionand just large enough to receive an abrasive stick I with suiiicientclearance to provide for ready movement of the abrasive stick. The anvil28 may be made in two or more parts welded, pinned' or bolted togetherfor ease of manufacture. At the left-hand side of the anvil 28 isattached a long support 22 which forms a slideway for a ratchet bar 23.The ratchet bar is of a size such that it can move into the hole 2|. ApaWl .24 pivoted at 25 on a bell crank lever 26 pivoted at 21 in a fork28 attached to the support 22 constitutes means for moving the ratchetbar 23 by the distance of one tooth for each actuation of the bell crank26 which may readily be operated by hand. A spring 29 normally moves thehandle 38 of the bell crank lever 26 upwardly. This spring 29 issupported by a U shaped standard 3| which straddles the bell crank lever26 and forms an upper stop for the bell crank lever 26. A lower stop forthe bell crank lever 26. is preferably provided, for example in the formof an angle bar 32 adjustably fastened at 33 to the support 22.

The operator may depress the handle portion 39 of the bell crank lever26 and thus move the ratchet bar 23 tothe right by a controlled amount.'I'he apparatus further includes a shear rod 35 supportedfor verticalmovement in a guide block 36 and normally held in the upper positionshown by a spring31. 'I'he shear rod 35 has a head 38 which is of fairlymassive construction. With a heavy-hammer the operator can strike thehead 38 which will move the rod 35 downwardly, striking a shearing blowagainst the projecting portion of the vitriiied stick l5. By alternatelymoving the bell crank lever 26 with one hand and striking the head 38,the operator can readily produce sheared particles of vitried abrasivematerial which are of equilateral triangular shape in cross section andof relatively short length as compared to one of the sides thereof. Forexample, a triangular prism of a length approximately one half of any ofits sides may be made in this manner. It may be noted that the shape ofthe hole 2| in the anvil 28 is such that the top part is a horizontalplane surface. The action is a shearing action and produces nearly aplane surface on the fractured pieces of bonded abrasive. These, becauseof their resemblance to irregularly shaped fragments of bonded abrasivematerial, I term aggregates 48. They differ from previously existingaggregates in that they are all of regular shape and specificallyequilateral triangular prisms.

I further provide a mold rotating apparatus, as shown in Figure 5. Thismay comprise a base 45 in which is supported a journal 46 having avertical axis in which is located a spindle 41 having keyed to its upperportion a table 48. I may provide a lower journal 49 for thc spindle 41and a thrust bearing 58. Keyed to the spindle 41 is'a gear 5| meshingwith a pinion 52 fastened to a shaft 53 which is journalled in upper andlower The pinion 52 may be formed on a sleeve 56 with which is alsointegrally formed a bevel gear 51 meshing with a bevel gear 58 securedto the armature shaft of an electric motor 59. 'Ihis is preferably adirect current motor which is connected by a conductor 68 to a suitablesource of direct current, such as a battery 6|, the other end of whichis connected by a conductor 62 to a rheostat 63, the movable part ofwhich constitutes a treadle 64 pivoted at 66. The contact 86 attached tothe treadle 64 and constituting part of the rheostat 83 is connected bya suitable conductor to a conductor 61 which is connected to the otherterminal of the motor 59. A suitable spring 18 may be provided normallyto hold the treadle 64 in the upper or full resistance position shown. Asuitable switch 1| is interposed in any of the conductors forming themotor circuit.

The operator may cause the table 48 to revolve by closing the switch 1|and thereafter may control its speed within limits by use of the treadle64. As shown in Figures 5 and 6, I provide further a more or lessconventional mold which may comprise an outer supporting plate 12, anannular mold ring 13, a mold bottom plate 14, a mold top plate 15, anouter top plate 16. and a mold plug 11. 'I'he outer supporting plate 12has a hole 18 in which ts a plug 19 fastened to the top of the spindle41 in order to center lthe mold on the table 48.

Placing the plug 11 in the bottom plate 14, as shown in Figure 5, withthe mold ring 13 around the bottom plate 14, I insert in the mold andagainst the bottom plate 14 an annular disk of unvulcanized rubbercompound 88. I then place these mold parts on the table 48, as shown inFigure 5. With the aidof a suitable hopper, shovel, trowel or othermanual implement, I scoop up a quantity of triangular aggregates 48 froma container or box in which they may have been collected and dump theminto the mold ring 13 on top of the rubber on the bottom plate 14. Iplace in the mold a quantity approximately sumcient to form a ring 8| ofaggregates 4l, all in contact with the mold ring 13. Centrifugal forcewill force the aggregates 48 against the ring 13 and by adding orsubtracting aggregates 48 and with the use of a stick or guide held inthe hand, a ring or circle 8| of aggregates located close together mayquickly be formed. The only way that the aggregates 48 can be assembledin a rotating mold in close spaced relation is with one side of eachalternate aggregate nearly tangent to' the circle of the mold ring 13,as shown. As quickly as one row 8| is formed, I introduce moreaggregates 48 and form another row 82. The procedure may be repeated forrows 83, 84, 85 and so on until the entire mold is filled withaggregates 48 to a depth of one layer, all of them being in orientedposition, as shown in Figure 7. I then place another annular disk |08 ofunvulcanized rubber compound on top of the aggregates 48 and place thetop plate 15 and outer mold plate 16 in position, as shown in Figure 6.I then close the mold in a suitable hydraulic press, strip the mold, andremove the pressed article and vulcanize it. The result is a grindingwheel which is shown in cross section in Figure 7, constitutingtriangular abrasive aggregates 48 oriented as shown in Figure 7 andbonded together with rubber bond. 'I'he rubber mixture for the annulardisks 88 and |88 preferably has enough sulphur to form a hard rubber andmay have a filler comprising a certain quantity of abrasive grain inorder to increase its hardness. In certain cases, however, a rubbermixture having no abrasive grain will preferably be used. The rubbercompound for the disks 88 and |88 may vary widely and any of the knownformulae for manufacturing rubber bond for rubber bonded grinding wheelsmay be used, many such formulae now being known to those skilled in thisart.

Considering the action of the abrasive wheel of Figure 7, which is acutting-on wheel, it will be seen that the triangular abrasiveaggregates are located so that sharp cutting edges face in bothcircumferential directions and as the wheel wears down, new sharpcutting edges are automatically provided. That is'to say, as eachtriangular aggregate 40a whose flat side is substantially tangent to theperiphery is reduced on that side by reason of wearing away of thewheel, it still presents a cutting edgerwhich is inclined thirty degreesto the radius of the wheel at that point, this being quite an effectivecutting edge. Intermediate aggregates Mib whose apexes abut .theperiphery fill the gaps between the other a`g gregates. They do somecutting on account of their abrasive action but the major portion of thecutting is done by theaggregates' 40a.- The rubber is forced between theseveral aggregates as the filling method described can be carried outvery readily without packing the aggregates iii too tightly. The rubber.being softer, wears away readily and provides' a Vclearness for thechips cut from the metal b'eing cut off.

By simply providing a higher mold ring 'I3 or thicker plates ld and 15,or' both, I can fill the mold of Figures and 6` with a plurality oflayers oi triangular aggregates 6B.' The top disk lill) of rubbercompound will form the bottom disk for the next layer. A wheel soconstructed is l shown in the fragmentary cross sectional view dit orFigure 8. This may be used for purposes other than cutting-ori andpreferably is, being particularly adapted for cylindrical or othergrinding where a relative reciprocatory traverse of wheel and work pieceis provided.

One feature oi the invention involves the formation and orientation ofabrasive particles which have cutting edges which will operatesubstantially as a lathe tool does, and preferably in both directions sothat it is immaterial in which direction the wheel is revolved. Withthis feature ci advantage is coupled a method of manufacture which canbe carried out without expensive equipment and at areasonable labor costso that the wheels shall not cost excessively more than those made bypreviously known methods.

While the oriented feature described herein in detail is a feature ofadvantage of `this invention, it will be understood that atriangular-prism on its side as distinguished from its edge constitutesan abrasive particle which presents a sharpedge in one direction ofrotation however it is oriented and accordingly, so far as certainfeatures of the invention are concerned, the shaped aggregates may beplaced in a mold haphazard without orientation and the wheel formedtherefrom will have excellent cutting properties.

lt will thus be seen that there has been provided by this invention anarticle, method and apparatus in which the' various objects hereinaboveset forth together with many thoroughly -practical advantages aresuccessfully achieved.

As various possible embodiments might be made of the mechanical featuresof the above invention and as the art herein described might be variedin various parts, all without departing from the scope of the invention,it is to be understood that all matter hereinbefore set forth or shownin the accompanying drawing is to be interpreted as illustrative and notin a limiting sense.

l'. clainn- 1. A grinding wheel comprising triangular abrasiveaggregates oriented with sides tangent to concentric circles of thewheel bonded together into an integral whole.

2. A. grinding wheel comprising abrasive aggregates equilateraltriangular prisms in shape and a bond holding the aggregates together inan integral structure with a great number of the triangular prismaggregates oriented so that one fiat side of each is substantiallytangent to a concentric circle of the wheel.

3. An abrasive body comprising a plurality of triangular aggregateprisms in like position and a plurality ofabrasive aggregate triangularprisms in similar opposed position interspersed between the first namedtriangular prisms in substantially regular order and bonded togetherwith bond. A

4. An abrasive wheel comprising a great number of 'aggregates eachcomprising abrasive grains bonded with vitriiied bond and in the shapeof -4 equilateral triangular prisms oriented so that substantially onehalf of the prisms have sides tangent to concentric circles of the wheeland the other half of said aggregates are likewise oriented,V the firsthalf having their apexes pointing inwardly and the second half havingtheir apexes 'pointing outwardly, and organic bond holding all of saidaggregates together in an integral wheel.

5. The method of making a grinding wheel which comprises pressing aquantity of abrasive grain and bond to form a stick which is atriangular prism, maturing the bond thereof, shearing.

off small sections of the triangular prism to form abrasive aggregatesof small thickness as respects any side thereof, and constitutingtriangular prisms in shape, providing a rotating mold, filling the moldslowly with aggregates to form a ring thereof against the periphery ofthe mold, continuing the filling to form additional rings until the moldis lled, incorporating suitable bond to bond the aggregates together,pressing and maturing.

GEORGE CROWTON, JR.

